Thanks, I won't be using it. My initial instinct was "NO!", but I wondered later if I was being paranoid. I wanted some feedback about whether this might actually be an ok source of protein. I usually add distiller's grain, which is a by-product of distilling alcohol, usually for drinking, sometimes for fuel, and it's worked out well for me.
But, I read some studies that had been done using DG. If the DG is a nice golden color, it's great. Increased growth, healthy animals, etc. However, if it's dark brown, or smells at all burnt or smoky, it has the opposite effect. Decreases growth, and so on. Lately, the DG available has been getting darker and darker, so I've stopped using it for now.
I went ahead and got a bag of soybean meal for now, as my 3 options are soybean, cottonseed, and DG. Maybe the DG will get lighter again soon.
I don't have a problem with the idea of using "by-products", as long as I know what they are, and have at least some idea how they're produced. We use a great many things everyday that are by-products of one process or another. Cream of tarter is a by-product of wine making. Bran is a by-product of grain milling (to make white flour). When I bake bread, I often use water from boiling potatoes, so you could say the potato water is a by-product of making mashed potatoes. Any kind of nut or seed that is pressed for oil, leaves a nutritious, protein-rich cake or meal behind, as a by-product. Some are more suitable than others, to feed either people or animals. I'm all for using as much of a thing as possible, and reducing waste, as long as it isn't something harmful.